linux: Get font DPI from GTK.

linux: Get font DPI from GTK.

Use GtkSettings's gtk-xft-dpi property to convert Pango font
descriptions from points to pixels. Previously
PangoContext's default resolution, which is sometimes
(always?) unset, was used, resulting in 96 DPI being used
for conversions regardless of the value reported by X.

BUG=375824
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=284121

[msw, 2014-07-18 03:39:33]

lgtm with nits; +cc oshima as per his related TODO:
https://code.google.com/p/chromium/codesearch#chromium/src/ui/views/widget/de...

https://codereview.chromium.org/406493002/diff/1/chrome/browser/ui/libgtk2ui/...
File chrome/browser/ui/libgtk2ui/gtk2_ui.cc (right):

https://codereview.chromium.org/406493002/diff/1/chrome/browser/ui/libgtk2ui/...
chrome/browser/ui/libgtk2ui/gtk2_ui.cc:665: gint dpi = 0.0;
nit: should this be -1 if for some reason g_object_get does nothing?

https://codereview.chromium.org/406493002/diff/1/ui/gfx/linux_font_delegate.h
File ui/gfx/linux_font_delegate.h (right):

https://codereview.chromium.org/406493002/diff/1/ui/gfx/linux_font_delegate.h...
ui/gfx/linux_font_delegate.h:47: // font sizes between points and pixels. -1 is
returned if the DPI is unset.
nit: return 96 instead of -1 here (vs in GetPangoDPI)?

https://codereview.chromium.org/406493002/diff/1/ui/gfx/pango_util.cc
File ui/gfx/pango_util.cc (right):

https://codereview.chromium.org/406493002/diff/1/ui/gfx/pango_util.cc#newcode91
ui/gfx/pango_util.cc:91: static bool determined_dpi = false;
nit: |dpi| can't be negative, init to -1 and s/determined_dpi/dpi<0/

https://codereview.chromium.org/406493002/diff/1/ui/gfx/pango_util.cc#newcode108
ui/gfx/pango_util.cc:108: static bool determined_value = false;
nit: ditto for |pixels_in_point| and |determined_value|

[Daniel Erat, 2014-07-18 04:20:26]

https://codereview.chromium.org/406493002/diff/1/chrome/browser/ui/libgtk2ui/...
File chrome/browser/ui/libgtk2ui/gtk2_ui.cc (right):

https://codereview.chromium.org/406493002/diff/1/chrome/browser/ui/libgtk2ui/...
chrome/browser/ui/libgtk2ui/gtk2_ui.cc:665: gint dpi = 0.0;
On 2014/07/18 03:39:33, msw wrote:
> nit: should this be -1 if for some reason g_object_get does nothing?

yep, and certainly not a double. thanks

https://codereview.chromium.org/406493002/diff/1/ui/gfx/linux_font_delegate.h
File ui/gfx/linux_font_delegate.h (right):

https://codereview.chromium.org/406493002/diff/1/ui/gfx/linux_font_delegate.h...
ui/gfx/linux_font_delegate.h:47: // font sizes between points and pixels. -1 is
returned if the DPI is unset.
On 2014/07/18 03:39:33, msw wrote:
> nit: return 96 instead of -1 here (vs in GetPangoDPI)?

i thought about this, but it seemed a bit cleaner to me to distinguish between
the unset and set-to-96 cases. gtk itself doesn't say what the default should
be: "Resolution for Xft, in 1024 * dots/inch. -1 to use default value."
(https://developer.gnome.org/gtk3/stable/GtkSettings.html#GtkSettings--gtk-xft...)

https://codereview.chromium.org/406493002/diff/1/ui/gfx/pango_util.cc
File ui/gfx/pango_util.cc (right):

https://codereview.chromium.org/406493002/diff/1/ui/gfx/pango_util.cc#newcode91
ui/gfx/pango_util.cc:91: static bool determined_dpi = false;
On 2014/07/18 03:39:33, msw wrote:
> nit: |dpi| can't be negative, init to -1 and s/determined_dpi/dpi<0/

good call; done

https://codereview.chromium.org/406493002/diff/1/ui/gfx/pango_util.cc#newcode108
ui/gfx/pango_util.cc:108: static bool determined_value = false;
On 2014/07/18 03:39:33, msw wrote:
> nit: ditto for |pixels_in_point| and |determined_value|

Done.

[oshima, 2014-07-18 04:24:22]

nice. We can use this to compute scale factor I guess?

Or should I use gdk_screen_get_monitor_scale_facotr()
instead?

https://developer.gnome.org/gdk3/stable/GdkScreen.html#gdk-screen-get-monitor...

[msw, 2014-07-18 05:02:33]

Still lgtm

https://codereview.chromium.org/406493002/diff/20001/ui/gfx/pango_util.cc
File ui/gfx/pango_util.cc (right):

https://codereview.chromium.org/406493002/diff/20001/ui/gfx/pango_util.cc#new...
ui/gfx/pango_util.cc:107: pixels_in_point = GetPangoDPI() / 72.0;  // 72 points
in an inch
nit: I guess you can inline the init with the decl.

[Daniel Erat, 2014-07-18 14:27:05]

https://codereview.chromium.org/406493002/diff/20001/ui/gfx/pango_util.cc
File ui/gfx/pango_util.cc (right):

https://codereview.chromium.org/406493002/diff/20001/ui/gfx/pango_util.cc#new...
ui/gfx/pango_util.cc:107: pixels_in_point = GetPangoDPI() / 72.0;  // 72 points
in an inch
On 2014/07/18 05:02:33, msw wrote:
> nit: I guess you can inline the init with the decl.

good point. thanks, done

[Daniel Erat, 2014-07-18 14:27:22]

The CQ bit was checked by derat@chromium.org

[commit-bot: I haz the power, 2014-07-18 14:27:52]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/derat@chromium.org/406493002/40001

[commit-bot: I haz the power, 2014-07-18 16:29:55]

Change committed as 284121